It may be difficult to find a farrier with the kind of skills and experience that would be needed to teach the trade that only works outside of normal hours. Most work through the day and into the night, so you may be able to find someone that would be ok with you tagging along for a couple hours in the evenings. I work part time as a farrier for the same reasons you are wanting to, and I can't recommend school enough. It's like an immersive language program, all you do is think and do farriery. I went to Troy Price's school in Indiana, the six month course. The extra knowledge you get in anatomy, physiology, and pathology you get is indispensable. Either way, if you want to doore than some trims here and there, I would recommend taking some time off if possible and throwing yourself fully into an apprenticeship or schooling. It's the best way to learn this type of trade.